Device and method for compartmental vessel treatment

ABSTRACT

An angioplasty balloon having an elastic constraining structure that partially expands with the balloon so that, at maximum balloon inflation, the constraining structure forms a pattern of channels or “pillows” on the balloon.

This application claims the benefit of Provisional Application No.61/313,600 (Attorney Docket No. 026728-000200US), filed on Mar. 12,2010, the full disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to the field of medical methods anddevices, more specifically to medical angioplasty balloon catheters anddevices intended to deliver active substances to body tissue.

Angioplasty balloons are one of the most commonly used tools for thetreatment of narrowed blood vessels. These balloons are typicallycylindrical when inflated and have different lengths and diameters toconform to different vessel sizes. The balloons are located at thedistal end of flexible catheters and delivered to a target site/lesionwhere they are inflated at high pressure, normally between 8-20atmospheres, in order to overcome the resistance of the lesion andachieve luminal expansion. Such high pressure angioplasty is oftenassociated with trauma to the vessel walls with a resulting highfrequency of vessel dissection (30%-40%), abrupt closure of the treatedvessel (5%-12%), and restenosis. Thus, when conventional angioplasty isused as a primary treatment for occluded vessels, restenosis can occurin about 50% of the cases. Therefore, in the vast majority of coronarytreatments, angioplasty is used as an initial treatment followed byplacement of a stents. Frequently, the stents are coated with drug andpolymer requiring the patient to take anti platelet therapy for extendedperiods, possibly lifelong. to limit the risk of stent thrombosis orblood clots. Anti platelet therapy increases the risk of bleeding and isexpensive. In addition, patient must stop the antiplatelet therapybefore any surgical intervention, thus increasing the risk of suddendeath and often precluding beneficial procedures.

Dissections in blood vessels treated by balloon angioplasty are verycommon. The dissection rate is estimated to be as high as 30% of allcases. Some of the dissections are severe and may require urgent surgeryor placement of additional stents. In addition, dissection maycontribute to poor long term clinical results and restenosis even if astent is placed in the treated lesion. Dissections are usuallyattributed to several mechanisms occurring during balloon inflationincluding shear forces applied on the vessel walls as the balloon pleatsunfold as well as the uneven balloon inflation which occurs as a resultof the non-symmetric nature of the vascular disease. During inflation,the balloon diameter increases in the radial direction as the foldedballoon unwraps. As the folded lobes of the balloon open, the layersslide over one another and apply tangential forces to the lesion and/orvessel wall which can abrade the lesion or vascular wall and in theworst instances cause dissections. As shown in FIGS. 1A-1C, a catheter10 is initially located in a region of plaque (P) in a blood vessel(BV). A balloon 12 on the catheter 10 has folded lobes which unfold asthe balloon is inflated, as shown in FIG. 1B. The layers of the foldedlobes move in opposite directions, as shown by the arrows in FIG. 1B,with the upper exposed layer tending to slide across the surface of thelesion or if present, exposed vascular wall. Such unintended lateralmovement of the balloon surface can occur until the balloon is fullyinflated, as shown in FIG. 1C.

Uneven inflation results from the uneven nature of the disease in thevessel. Angioplasty balloons are commonly non-compliant orsemi-compliant, and when semi-compliant balloons are inflated against aneccentric lesion, the balloon will follow the “path of least resistance”and its diameter will increase more in the less diseased sections of thevessel, often increasing trauma in these areas.

For these reasons, it would be desirable to provide improved balloonsand inflation structures for angioplasty balloons used in vasculartreatments. In particular, it would be desirable to provide angioplastyballoons having a reduced tendency to cause trauma and dissection in theblood vessel walls as the balloon is inflated by modulating theinflation characteristics of the balloon and provide a segmentedcompartmental dilatation with local areas of compliance. It would befurther desirable if the reduced dissections could also reduce the riskof elastic recoil and abrupt reclosure which are associated with currentangioplasty balloons and their use. It would be further desired if suchimproved angioplasty balloon structures were compatible with each ofstents, drug-eluting stents, and drug coated balloons. These advantageswould preferably be obtained without loss of the ability of thecatheters to increase the luminal size and restore blood vessel in thepatient being treated. At least some of these objectives will be met bythe invention as described hereinafter.

2. Description of the Background Art

U.S. Pat. Nos. 6,245,040 and 5,735,816, show balloon catheters havingelastic spiral restraints which form spiral indentations in the balloonwhen inflated. Other patents of interest include U.S. Pat. Nos.7,708,748; 7,686,824; 5,863,284; 5,772,681; 5,643,210; and 5,987,661.

BRIEF SUMMARY OF THE INVENTION

The present invention comprises a device for angioplasty or dilatationof stenotic vessels and optionally for the delivery of active substanceto the vessel walls. A balloon catheter is designed to modulate theinflation characteristics of the balloon to provide a segmentedcompartmental dilatation with local regions of compliance capable ofconforming to the uneven nature of the vascular disease. The ballooncatheter of the present invention includes a constraining structure (CS)located over a balloon on a distal end of the catheter. The CS serves tocontrol and limit balloon inflation and modify balloon topography,typically by forming protruding regions (“pillows”) over the surfacethat cause local dilatation in a small region of the vessel independentof those formed by neighboring protruding regions. Such discreteprotruding regions will each separately engage a segment of the lesionwhen the balloon is inflated so that the pressure and degree of balloonexpansion applied against that segment is controlled and limited, thusreducing the risk of trauma while assuring that all segments of thelesion are adequately treated. The lesion can be uniformly treated alongits length while excessive pressure against any one segment of thelesion can be reduced or avoided entirely. Such local dilatation avoidsthe “path of least resistance” phenomenon described above and allowslocal and non-uniform treatment for different sections or regions of thevessel, where the modified balloon topography minimizes trauma andinjury of vessel wall as the balloon is inflated to the very highpressures associated with angioplasty. The CS also inhibits transfer ofshear forces to the lesion and vessel wall as the balloon inflates andthe wall layers open and slide laterally relative to the vessel wall.Conventional balloons present a continuous surface across the treatedsection of the vessel (sometimes as long as 200 mm to 300 mm inperipheral lesions) that leads to balloon deformation and uneven alongthe treated segment. Such an “aggregated dilatation” mechanism whenapplied to a diseased vessel having an uneven lesion geometry increasesthe probability of trauma and dissection. In contrast, the balloon ofthis invention provides for a more localized but balanced forcedistribution (e.g., as a result of the uniformly distributed protrudingregions) along the length of the disease even when the disease variessignificantly in size over its length.

In one embodiment of this invention, the CS is situated over thedeflated and folded balloon and attached to a shaft of the catheter neara distal end of the balloon, near a proximal end of the balloon, orpreferably both. The CS does not have to be attached to the balloon andcan float over the folded balloon optionally having elastic covers ateither or both ends (e.g., covers made of polymer). Upon ballooninflation, the CS expands to its maximum diameter and allows the balloonto further inflate through openings in the CS in a preselected pattern.Upon device deflation, the CS will elastically close to its originaldiameter.

In one embodiment of the invention as the balloon inflates, both theballoon and CS increase in diameter. The CS maximal open diameter,however, is smaller than fully inflated balloon diameter thus ballooncontinues to expand through the openings in the CS creating a series ofprotruding regions, typically in an orthogonal or diamond “quilted”pattern. The CS has a relatively small diameter before expansion and iscapable of expanding due to inflation force applied by balloon expansionto a diameter smaller than that of the fully inflated balloon. The CSexpansion is limited by its geometrical design.

The CS is designed to control balloon inflation by limiting andrestricting balloon diameter across the treated segment in a way thatwill eliminate large diameter differences during the inflation process.Thus, when balloon pressure is increased, as is commonly done in orderto overcome local narrowing, overstretching other parts of the treatedlesion can be reduced or avoided entirely In addition, the CS can reduceor eliminate the transfer of tangential forces resulting from unfoldingof the balloon against the vessel wall. The CS creates a network ofcrossing channels with protruding regions or “pillows” therebetween. Thechannels between the protruding regions prevent high radial stressbuildup by providing stress relief regions between adjacent protrudingregions. The stress relief regions can stretch or expand without beingsubjected to direct balloon surface contact thus minimizing traumacaused to vessel walls during inflation. In addition, the channels allowfor plaque extrusion (redistribution) thus adding a new mechanism inaddition to simple compression mechanism of conventional balloons.

In a first aspect, the present invention provides a system forperforming angioplasty. The system includes a catheter shaft having aninflatable balloon at its distal end and a constraining structuredisposed over the inflatable balloon. The constraining structure has anon-expanded configuration where it lies closely over or within folds ofthe balloon prior to inflation and an expanded configuration which issmaller than an unconstrained size of the balloon (when fully inflated)so that the structure restrains the balloon inflation along a pluralityof crossing channel lines. By “crossing” channel lines, it is meant thatthe channels will intersect at a plurality of locations so that thechannels comprise an intersecting matrix of interconnected channels.Individual channel lines may be oriented axially, circumferentially, orpreferably will include channel lines with both axial andcircumferential orientations where the axial channels intersect thecircumferential channels. Alternatively, the channels could be formed astwo or more counter wound helical channels that intersect to formdiamond-shaped protruding regions.

In specific preferred embodiments, the constraining structure willcomprise a plurality of circumferentially spaced-apart axial struts anda multiplicity of axially spaced-apart radially expandable ringsattached to the axial struts. The rings are joined to the struts atintersecting angles, preferably in the range from about 75° to 105°. Inparticularly preferred embodiments, the intersecting angles will be 90°.The axial struts will be coupled to the catheter on both a distal sideof the balloon and on a proximal side of the balloon. In someembodiments, at least one of the distal strut ends and the proximalstrut ends will be free to translate axially over the catheter shaft asthe balloon is inflated (to accommodate foreshortening which wouldotherwise occur). Alternatively, the individual struts may be fixedlyattached to the catheter shaft on both the proximal and distal side ofthe balloon where the struts are elastic or otherwise stretchable intension so that they will elongate as the balloon is inflated. Forexample, axial struts could be composed of an elastomer or other elasticmaterial which allows elongation. More typically, the axial struts wouldinclude features, such as zig-zags, S-shaped links, coil springs, or thelike, which would accommodate elongation (if needed) when either or bothof the strut ends are attached to the catheter shaft.

The radially expandable rings will also be formed so that they canstretch or elongate to increase in diameter as the balloon is inflatedin the ring. The expandable rings could be formed from inherentlyelastic materials, such as stretchable polymers or the like, but moretypically will be formed with expansible features which allow the ringto expand when the balloon is inflated. The expandable features can bethe same as with the axial struts, including zig-zags, S-shaped curves,coils, and the like. In all cases, it is necessary that the rings havean maximum diameter beyond which they will not further increase in sizeas the balloon is inflated. When the rings are formed with expandablefeatures, the maximum ring expansion will occur when these features arefully elongated. If an elastomeric or other material is used to form therings, non-distensible tethers or other expansion limits can be builtinto the rings so that they do not exceed their desired maximumdiameter.

The balloons may also be coated or otherwise adapted to deliver drugs.Techniques for coating balloons with drugs are well described in thepatent literature. See, for example, U.S. Pat. No. 7,750,041;US2010/02280228; US2010/0278744; and US2008/0102034, the fulldisclosures of which are incorporated herein by reference.

In a second aspect, the present invention provides a method for treatinga lesion in a blood vessel. The method comprises inflating a balloonwithin the blood vessel where the balloon is constrained along aplurality of crossing channel lines, typically axial and/orcircumferential channel lines which intersect and cross each other. Thechannel lines create a number of isolated protruding regions in theballoon, where the protruding regions contact the lesion while thechannel lines are recessed away from the vessel wall. “Recessed” meansthat the bottom or trough of the channel line will be positionedradially closer to the axis of the catheter than is the inflated surfaceof the balloon. In many cases, the bottoms of the channels will notcontact the lesion or blood vessel wall. In other cases, however,particularly when the plaque or thrombosis being extruded, the channelsmay fill with the lesion material while providing the benefits of stressrelief described above since the bottoms of the channels will remainspaced radially inwardly from the blood vessel wall.

The balloon will typically be composed of a non-distensible orsemi-compliant material so that it may be inflated at relatively highpressures, typically in the range from 10 atmospheres to 25 atmospheres,without over expanding within the blood vessel. Thus, both the balloon(when non-distensible) and the constraining structure will have maximumdiameters when the balloon is fully inflated where the difference in themaximum diameters defines the depth of the channels which are formed inthe balloon surface. The protruding regions will often have similarsizes (±50% of area engaging the lesion) and will be uniformlydistributed over the balloon surface. The balloons may be used forangioplasty, without subsequent stent delivery and/or drug delivery.Alternatively, the balloons may be used for expanding a stent, includingboth drug-coated stents and uncoated stents. Finally, the balloons maythemselves be coated with drug in order to transfer drug to the lesionor vessel wall during the treatment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1C show a cross-section of the stages of unwrapping ofconventional balloon inflation in a stenotic blood vessel.

FIGS. 2A, 2B1 and 2B2 show a constraining structure located on a balloonprior to inflation (FIG. 2B1) and after inflation (FIGS. 2A and 2B2).

FIGS. 3A and 3B illustrate a first exemplary ring structure where thering segments between adjacent axial struts are formed in a zig-zagpattern.

FIGS. 4A and 4B illustrate a first exemplary ring structure where thering segments between adjacent axial struts are formed in a S-shapedpattern.

FIGS. 5A and 5B illustrate a first exemplary ring structure where thering segments between adjacent axial struts are formed as a coil spring.

FIGS. 6A to 6C show a cross-section of the dilatation device in thisinvention during three stages of inflation with the balloon unwrappingwithin the constraining device.

FIGS. 7A and 7B show finite element analyses of the vessel trauma of aconventional balloon and the device described in this invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a device for treating of diseased,blocked, occluded or stenotic lumens in the body, typically bloodvessels including both arteries and veins, and more typically coronaryand peripheral arteries. This device dilates occluded vessels whileminimizing trauma to the lesion and luminal wall and reducing the riskof vessel trauma and injury. By placing an “elastic” constrainingstructure (CS) over a balloon of a balloon catheter, inflation of theballoon is controlled during balloon inflation and refolding of theballoon is aided as the balloon is deflated. The CS is designed toexpand to a diameter smaller than the maximal diameter of the balloonwhen fully inflated. The CS structure applies radial resistance toinflation and is thus able to constrain the balloon and distribute orbuffer the internal high pressure applied by the balloon to the luminalwall thus providing a controlled and less traumatic dilation process.The balloon which is typically formed from a non-distensible materialsuch as a polyamide or a polyether block amide, will preferably benon-distensible or semi-compliant with a stretchability below 10% withintypical inflation pressure ranges and a fully inflated size sufficientlylarge so that regions protrude through passages in the CS to formprotruding regions which engage and dilate the lesion.

The CS can be coupled or otherwise connected to the catheter shaft onthe distal side and/or the proximal side of the balloon. Alternatively,the CS can float over the balloon without fixed attachment using simplecovers or constraints, and the CS is preferably designed to maintain itslength during expansion of the balloon to limit relative axial movementbetween the CS and the balloon. The CS can be fabricated from variousmaterials using suitable processes and designs. The CS can be made frommetal, preferably an elastic metal such as a nickel-titanium alloy(Nitinol®) and/or from a variety of polymers (e.g., Nylon). For example,the CS can be constructed from wires or can be laser cut from a tube,sheath or other forms of materials.

In a preferred embodiment of this invention, the CS structure is locatedon the balloon and is expanded during balloon inflation. The CS expandsto a smaller diameter than the balloon thus constricting ballooninflation within a cylindrical cage. Parts of the balloon, however, keepexpanding through openings in the case of the CS creating controlleddilatation pattern and reducing or eliminating shear forces.

Once the CS reaches its maximum diameter (which is smaller than themaximum inflated balloon diameter), the balloon continues to inflatethrough openings in the CS creating a topography of protruding regions(hills) and channels (valleys) at the surface of the device, where thepattern of channels is defined by the geometry of the CS. The CScontributes to a controlled dilation process avoiding over expansion andminimizing the shear forces and uniform high pressure applied on thevessel wall as will be described in greater detail below with referenceto FIGS. 6A-6C and 7.

Referring now to FIGS. 2A, 2B1 and 2B2, an exemplary constrainingstructure 14 constructed in accordance with the principles of thepresent invention comprises a plurality of axial struts 16 and axiallyspaced-apart radially expandable rings 18. When the balloon 12 and thecatheter 10 is in its non-inflated state (as illustrated in FIG. 2B1),the balloon is folded with a number of overlapping lobes, as best seenin FIG. 6A (discussed below). The constraining structure 14 has agenerally cylindrical geometry with a diameter just large enough tocover the deflated balloon 12.

As the balloon 12 is inflated, as illustrated in FIGS. 2A and 2B2, theradially expandable rings 18 expand in response to the force of theballoon. The rings will be structured, however, so that they reach amaximum diameter beyond which they will no longer radially expandregardless of the continued inflation or expansion of the balloon. Asthe axial struts 16 are attached or otherwise coupled to the radiallyexpandable rings 18, the radially outward travel of the struts is alsolimited to a distance defined by the maximum diameter of the rings.Thus, as the balloon will have a fully inflated diameter which is largerthan that of the maximum diameter of the radially expandable rings 18,when the balloon is fully inflated a plurality of axial andcircumferential channels 20 and 22, respectively, will be formed in theballoon surface. A plurality of protruding regions 24 (as seen in FIG.2B2) are defined in the openings or in interstices between the adjacentaxial struts 16 and radially expandable rings 18. It is these protrudingregions 24 which provide the benefits of the present invention asdescribed above.

The axial struts 16 and radially expandable rings 18 of the constrainingstructure 14 are illustrated as simple straight beams or elements, itwill be appreciated that they need to have some elasticity orstretchability in order to accommodate the radial expansion of theballoon and the radial increase in size of the rings. While the axialstruts 14 need only be flexible since they can be free to slide alongthe catheter shaft 26 at either or both of the proximal and distal ends,the rings 18 must have the ability to elongate in the circumferentialdimension as the balloon increases in diameter, although the rings willhave a maximum diameter beyond which they will not expand, as discussedabove. Most simply, the axial struts 16 and/or the radial expansionrings 18 may be formed from an elastic material which is capable ofelongating under a tensile force, such as an elastomeric polymer, a coilspring, or the like. If such materials and/or structures are used withthe radially expandable rings, however, there must also be a separatenon-distensible or non-stretchable component which provides for theradial expansion limit.

Alternatively, the axial struts 16 and/or the radially expansible rings18 may be formed from a generally non-stretchable material, typically ametal such as a nickel-titanium alloy as noted above, and be providedwith features or patterns which allow for elongation under a tensileforce. For example, as illustrated in FIGS. 3A and 3B, the radiallyexpandable rings 18 could be formed in a zig-zag pattern so that theycan elongate from a shortened configuration, as shown in FIG. 3A, to afully elongated configuration, as shown in FIG. 3B. Although notillustrated, it will be appreciated that the axial struts could employthe same geometric features allowing for axial elongation. Shown inFIGS. 4A and 4B, the rings 18 could be provided with S-shaped orserpentine structures which allow for elongation from a shortenedconfiguration (FIG. 4A) to a fully elongated configuration (FIG. 4B)corresponding to the fully expanded diameter configuration shown inFIGS. 2A and 2B2. Alternatively, the rings 18 could be provided with acoil configuration, as shown in FIGS. 5A and 5B, where the coil willassume a shortened configuration when the ring is at its minimumdiameter, as shown in FIG. 5A, and will stretch to accommodate a fullyexpanded configuration, as shown in FIG. 5B. The coil springs, however,like the elastic polymer embodiments described above will in mostinstances require a separate element or component to prevent expansionbeyond the desired maximum limit.

Referring now to FIGS. 6A through 6C, the catheter 10 carrying theballoon 12 and constraining structure 14 is introduced to a region ofplaque P and a blood vessel BV in a generally conventional manner. Oncethe balloon 12 and constraining structure 14 are at the target location,the balloon is inflated, causing the constraining structure 14 toradially expand until it reaches a maximum diameter, as shown in FIG.6B. Once it has reached its maximum diameter, the constraining structure14 will no longer expand, but portions of the balloon 12 which arelocated in the open regions between adjacent axial struts and radiallyexpandable rings will continue to expand until reaching their maximumexpansion, as shown in FIG. 6C, where the fully formed protrudingregions 24 are present. As the balloon 12 will typically be formed froma non-distensible material, as noted above, once the maximum balloonsize has been reached further balloon inflation will not significantlyincrease the balloon size.

FIGS. 7A and 7B show finite element analyses of the forces applied onthe vessel wall comparing a conventional balloon (FIG. 7A) with thedevice of the present invention (FIG. 7B). The conventional balloondisplays uniform high strains in contrast to the balloon of thisinvention which displays stretching in the areas where the tissue isfree from contact with the balloon. The uniform balloon pressure isreplaced with an alternating pressure pattern that reduces vesseltrauma.

The present invention can be utilized to deliver various agents oractive substances particularly (but not limited to) those suitable fortreating vascular and other luminal conditions such as antiproliferativeand antimitotic agents (such as paclitaxel and sirolimus) othersubstances can include antibiotics, antiplatelet agents hormones andmore.

The active substance can be placed in various designs or techniques suchas directly coated on the balloon surface, the CS or both. It can beembedded in a matrix/carrier placed on the balloon or the CS or both.The combination of low trauma dilatation with release of active agentcan be superior to drug eluting stents for some portions of thepopulation by minimizing the need for a permanent implant yet providinggood long term results.

In one embodiment the balloon surface is coated with drug. Upon ballooninflation, the protruding regions formed in the balloon external surfacecoated with drug engage the vessel wall and compress the drug into thewall to facilitate efficient drug delivery to the treated site.

Drug delivery can be facilitated using many different design methodsincluding but not limited to coating the balloon, coating the CSstructure or both. Coating with a drug directly or using a carrier in aform of a matrix or microcapsules.

While the above is a complete description of the preferred embodiment ofthe invention, various alternatives, modifications, additions andsubstitutions are possible without departing from the scope thereof,which is defined by the claims.

1. (canceled) 2.-23. (canceled)
 24. A balloon catheter comprising: acatheter shaft; a balloon on the catheter shaft; and a constrainingstructure disposed over the balloon, the constraining structure fixedlyattached to the catheter shaft distal of the balloon and/or proximal ofthe balloon to prevent detachment of the constraining structure from thecatheter shaft, the constraining structure comprising a plurality ofopenings; wherein the constraining structure is configured to transitionbetween an unexpanded configuration and an expanded configuration;wherein inflation of the balloon expands the constraining structure tothe expanded configuration with a plurality of isolated balloon regionsprotruding from the plurality of openings, the plurality of isolatedballoon regions configured to contact a wall of a blood vessel with theconstraining structure displaced from the wall of the blood vessel. 25.The balloon catheter of claim 24, wherein the constraining structure isfixedly attached to the catheter shaft distal of the balloon andproximal of the balloon.
 26. The balloon catheter of claim 24, wherein,prior to inflation of the balloon, the balloon is folded beneath theconstraining structure.
 27. The balloon catheter of claim 24, whereinthe balloon is coated with a drug.
 28. The balloon catheter of claim 24,wherein the constraining structure is coated with a drug.
 29. Theballoon catheter of claim 24, wherein the plurality of isolated balloonregions are uniformly distributed over a surface of the balloon.
 30. Theballoon catheter of claim 24, wherein the constraining structurecomprises a polymer material.
 31. The balloon catheter of claim 24,wherein the constraining structure comprises an elastic material. 32.The balloon catheter of claim 24, wherein the balloon comprises asemi-compliant material.
 33. The balloon catheter of claim 24, whereinthe plurality of isolated balloon regions are diamond shaped.
 34. Aballoon catheter comprising: a catheter shaft; a balloon on the cathetershaft; and a constraining structure disposed over the balloon, theconstraining structure fixedly attached to the catheter shaft distal ofthe balloon and/or proximal of the balloon to prevent detachment of theconstraining structure from the catheter shaft; wherein inflation of theballoon expands the constraining structure to create a plurality ofisolated balloon regions separated by a plurality of intersectingchannels formed by the constraining structure; wherein the plurality ofisolated balloon regions are configured to contact a wall of a bloodvessel with the constraining structure displaced from the wall of theblood vessel.
 35. The balloon catheter of claim 34, wherein theplurality of intersecting channels comprise two or more helicalchannels.
 36. The balloon catheter of claim 34, wherein the plurality ofintersecting channels comprise a plurality of axially oriented channels.37. The balloon catheter of claim 34, wherein the plurality ofintersecting channels comprise a plurality of circumferentially orientedchannels.
 38. The balloon catheter of claim 34, wherein the plurality ofintersecting channels comprise a plurality of axially-oriented channelsintersecting a plurality of circumferentially oriented channels.
 39. Theballoon catheter of claim 34, wherein at least some of the plurality ofintersecting channels intersect to form an angle between 75 degrees and105 degrees, inclusive.
 40. The balloon catheter of claim 34, wherein,prior to inflation of the balloon, the balloon is folded beneath theconstraining structure.
 41. The balloon catheter of claim 34, whereinthe balloon is coated with a drug.
 42. The balloon catheter of claim 34,wherein the constraining structure is coated with a drug.
 43. Theballoon catheter of claim 34, wherein the balloon comprises asemi-compliant material.